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Semi-Annual Inspections for Insect and Water Damage

by Jack DeAngelis, PhD of

Water, not insect damage, is the single most important threat to most homes!

Water allows wood rot (called dry rot, ironically) fungi to develop that destroys the structural integrity of wood. Wood becomes weak and fragile as the fungus destroys its internal girders. Dry rot fungus needs high moisture in order to grow. Dry wood does not support fungal growth but the fungus can transport water from wet areas into dry wood through its branches (hyphae) thereby supporting growth and further wood decay. Advanced dry rot looks like “alligator skin” with its blocky appearance. If you detect dry rot you must locate and eliminate the source of water, replace rotted wood then treat surrounding wood with sodium borate (visit that kills the fungus. Water problems are best detected during the wet season. For most of us, this is the winter.

Certain insects are the next most important threats to your home's structural integrity once any water problems have been found and eliminated. Pay special attention to subterranean termites, carpenter ants and powderpost beetles. While other insects can cause minor damage these three account for most of the serious structural damage.

Subterranean termites...

Subterranean termites, “subs”, live in colonies in the soil and move into the structure through shelter tubes made of mud that are built on posts and foundation walls. Termites actually consume the wood directly. Wood damage can occur rapidly from a large colony. Termite infestations are usually found by observing these mud tubes.

The graphics below are a worker termite and a winged "reproductive" termite.  The workers do the actual damage to your home, taking bits of wood to provide food for the entire nest.  The reproductives migrate or "swarm" from the nest to establish new colonies.

Carpenter ants build their nests in wall voids and between floor joists. Damage occurs when these large, powerful ants expand their nests, destroying the surrounding structure. Carpenter ants do not eat wood, instead they forage for food outside the nest. Carpenter ants are best detected during warm months of the year when they form trails between the house and the outdoors in search of food.

The graphics below show termite damage (left) and carpenter ant damage (right).  Note that termites leave debris in their tunnels while carpenter ant tunnels are kept clear.

Powderpost beetles damage both hardwoods like maple, oak and ash, and softwoods like pine, spruce and fir. Structural damage, however, generally only occurs in softwood beams and joists. Damage to structural timbers by powderpost beetles is most common in damp coastal climates. Eggs are laid on the surface of wood. Hatching larvae (grubs) burrow into the wood where they consume the starch stored in wood cells. Once development is complete, in months to years, adult beetles emerge through holes they cut in the wood's surface. Powderpost beetle infestations are usually detected by these emergence holes. Beetles are less often found. Emerging beetles can re-infest the wood from which they emerge thus setting up an on-going infestation.

The best way to protect your house from water and structural insect damage is by doing semi-annual inspections. During summer inspect for carpenter ants, during winter inspect for water infiltration and dry rot, termites shelter tubes and powderpost beetle emergence holes. Use the form below.

Sample Inspection Form

Print this form and use it to guide your inspections for insect and water damage. Date the form after your inspection and put it in a safe place for future reference.

Date of Inspection:____________________

Exterior Inspection for Carpenter Ants During Summer

Walk slowly around the exterior. Do inspections in the morning or evening during warm months of the year. Remove all vegetation that touches any part of the structure including branches overhanging the roof. Look for trails of ants on exterior walls or on anything attached to the structure like decks. If there is a problem carpenter ants will be moving toward or away from the structure. If ants are found, collect a few for identification.

If ants were found trailing into or out of structure, describe location. _____________________________

What type of ant was found and where was the identification done? _____________________________

Exterior Inspection for Water During Winter

The main reason for this inspection is to check for water seeping into the structure from saturated soil. Forget about insect damage. Water, whether it comes from a leaky pipe, clogged gutter or up from the ground, is the biggest preventable threat to your home. Check foundation walls for water stains (Fig. 1) indicating water wicking up from the soil. If evidence of saturated soil is found, steps should be taken to reduce this water by improving drainage.

If evidence of saturated soil was found, describe location. _______________________________________

Crawlspace Inspection for Water, Powderpost Beetles and Termites During Winter

If you have a crawlspace do an inspection during the winter months. You will be able to check for water leakage through foundation walls that may not be evident during the summer. Also, check for termite mud shelter tubes on foundation walls, support walls and posts (Fig 2). Inspect anything that spans between the soil and the structure. Use a heavy screwdriver to tap on any structural members that appear damaged, or wet, in order to test their integrity. Finally check for powderpost emergence holes in floor joists and support beams.

If water seepage was found in the crawlspace, describe location. _________________________________

Was evidence of termites or powderpost beetles found, describe?_________________________________

Interior Inspections for Insect Activity

Check under sinks for water damage and evidence of insect activity. Check the attic (if accessible) for insect activity. This is the least important inspection but unfortunately the only one that most people do!

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